A gas turbine engine generally includes a compressor section, a combustion section, a turbine section, and an exhaust section. The compressor section progressively increases the pressure of a working fluid entering the gas turbine engine and supplies this compressed working fluid to the combustion section. The compressed working fluid and a fuel (e.g., natural gas) mix within the combustion section and burn in a combustion chamber to generate high pressure and high temperature combustion gases. The combustion gases flow from the combustion section into the turbine section where they expand to produce work. For example, expansion of the combustion gases in the turbine section may rotate a rotor shaft connected, e.g., to a generator to produce electricity. The combustion gases then exit the gas turbine via the exhaust section.
The turbine section includes one or more turbine nozzles, which direct the flow of combustion gases onto one or more turbine rotor blades. The one or more turbine rotor blades, in turn, extract kinetic energy and/or thermal energy from the combustion gases, thereby driving the rotor shaft. In certain configurations, each of one or more turbine nozzles define one or more internal passages that route cooling air therethrough and into a cavity where the rotor shaft is positioned to cool that turbine nozzle and the rotor shaft. Since the one or more turbine nozzles are in direct contact with the combustion gases and the cooling air is in direct contact with the one or more turbine nozzles, the temperature of the cooling air increases appreciably while flowing through the one or more turbine nozzles. This increase in the temperature of cooling air requires an increase in the volume of the cooling air to cool the rotor shaft, which may be undesirable.